Time dependent partial waves and vortex rings in the dynamics of wave packets

Time-dependent wave packet simulations of transport through Aharanov-Bohm rings with an embedded quantum dot

We have performed time-dependent wave packet simulations of realistic Aharonov-Bohm (AB) devices with a quantum dot embedded in one of the arms of the interferometer. The AB ring can function as a measurement device for the intrinsic transmission phase through the quantum dot, however, care has to be taken in analyzing the influence of scattering processes in the junctions of the interferometer arms. We consider a harmonic quantum dot and show how the Darwin-Fock spectrum emerges as a unique pattern in the interference fringes of the AB oscillations.

Mesoscopic Vortex-Meissner currents in ring ladders

Recent experimental progress have revealed Meissner and Vortex phases in low-dimensional ultracold atoms systems. Atomtronic setups can realize ring ladders, while explicitly taking the finite size of the system into account. This enables the engineering of quantized chiral currents and phase slips in-between them. We find that the mesoscopic scale modifies the current. Full control of the lattice configuration reveals a reentrant behavior of Vortex and Meissner phases. Our approach allows a feasible diagnostic of the currents' configuration through time of flight measurements.

Relativistic vortex electrons: paraxial versus non-paraxial regimes

A plane-wave approximation in particle physics implies that a width of a massive wave packet $σ_{\perp}$ is much larger than its Compton wavelength $λ_c = \hbar/mc$. For Gaussian beams or for packets with the non-singular phases (say, the Airy beams), corrections to this approximation are attenuated as $λ_c^2/σ_{\perp}^2 \ll 1$ and usually negligible. Here we show that this situation drastically changes for particles with the phase vortices associated with an orbital angular momentum $\ell\hbar$. For highly twisted beams with $|\ell| \gg 1$, the non-paraxial corrections get $|\ell|$ times enha…

Creating vortex rings and three-dimensional skyrmions in Bose-Einstein condensates

We propose a method of generating a vortex ring in a Bose-Einstein condensate by means of electromagnetically-induced atomic transitions. Some remnant population of atoms in a second internal state remains within the toroidal trap formed by the mean field repulsion of the vortex ring. This population can be removed, or it can be made to flow around the torus (i.e. within the vortex ring). If this flow has unit topological winding number, the entire structure formed by the two condensates is an example of a three-dimensional skyrmion texture.

Intrinsic multipole moments of the non-Gaussian wave packets

The charged wave packets with non-Gaussian spatial profiles are shown to possess intrinsic multipole moments. The magnetic dipole moment and the electric quadrupole moment are found for a wide class of the packets, including the vortex electrons with orbital angular momentum $\ell$, the Airy beams, the so-called Schrödinger's cat states, and their generalizations. For the packets with no phase vortices, the electric quadrupole moment is shown to grow quadratically with the packet's width, $|Q_{αβ}| \sim e\cdot σ_{\perp}^2$, while it is also $|\ell|$ times enhanced for the vortex beams. For ava…

Non-linear quantum effects in electromagnetic radiation of a vortex electron

There is a controversy of how to interpret interactions of electrons with a large spatial coherence with light and matter. When such an electron emits a photon, it can do so either as if its charge were confined to a point within a coherence length, the region where a square modulus of a wave function $|ψ|^2$ is localized, or as a continuous cloud of space charge spread over it. This problem was addressed in a recent study R.~Remez, et al., Phys. Rev. Lett. {\bf 123}, 060401 (2019) where a conclusion was drawn in favor of the first (point) interpretation. Here we argue that there is an alterna…

使用完美涡旋光束通过环芯光纤传输光通信信号

Transmission of optical communication signals through ring core fiber using perfect vortex beams

本文实验研究了完美涡旋光束和 Laguerre-Gaussian 光束在环芯光纤中的生成与传输特性，发现完美涡旋光束能减小环半径变化并耦合更高光功率，从而降低通信链路功率要求，为高维量子通信奠定基础。

Dynamical enhancement of nonparaxial effects in the electromagnetic field of a vortex electron

A quantum state of an electron influences its electromagnetic field. If a spatial profile of the electron wave packet is not Gaussian, the particle may acquire additional intrinsic multipole moments, which alter its field, especially at small distances. Here the fields of a vortex electron with orbital angular momentum $\ell$ are obtained in a form of a multipole expansion with an electric quadrupole term kept by using the generalized (non-paraxial) Laguerre-Gaussian beams. The quadrupole contribution arises beyond a paraxial approximation, is linearly enhanced for highly twisted packets with …

Semiclassical Dynamics of Electron Wave Packet States with Phase Vortices

We consider semiclassical higher-order wave packet solutions of the Schrodinger equation with phase vortices. The vortex line is aligned with the propagation direction, and the wave packet carries a well-defined orbital angular momentum (OAM) $\hbar l$ ($l$ is the vortex strength) along its main linear momentum. The probability current coils around momentum in such OAM states of electrons. In an electric field, these states evolve like massless particles with spin $l$. The magnetic-monopole Berry curvature appears in momentum space, which results in a spin-orbit-type interaction and a Berry/Ma…

Engineering vortex rings and systems for controlled studies of vortex interactions in Bose-Einstein condensates

We study controlled methods of preparing vortex configurations in atomic Bose-Einstein condensates and their use in the studies of fundamental vortex scattering, reconnection processes and superfluid sound emission. We explore techniques of imprinting closed vortex rings by means of coherently driving internal atomic transitions with electromagnetic fields which exhibit singular phase profiles. In particular, we show that a vortex ring can be prepared in a controlled way by two focused co-propagating Gaussian laser beams. More complex vortex systems may also be imprinted by directly superposin…